The present invention relates generally to combine harvesters and, more particularly, to a rotary cleaning device in combines for cleaning unwanted residue from threshed grain.
Conventional cleaning systems clean threshed grain by blowing air through a set of planar sieves utilizing gravitational forces to urge cleaned grain through the sieve openings. With the advent of higher capacity threshing and separating mechanisms, such as rotary axial flow combines, the capacity for threshing grain has increased beyond the capacity of conventional cleaning systems to clean the grain. Accordingly, it is desirable to increase both the capacity and the efficiency of cleaning systems in combine harvesters so as not to limit the throughput capability of the combine.
Rotary cleaning devices utilizing centrifugal forces to increase throughput capacity must have the grain to be cleaned in contact with the sieves to enable the centrifugal force to urge the cleaned grain through the sieves. Threshed grain parting from its contact with the sieves can become airborne with the unwanted residue and be discharged from the combine and/or fall rearwardly on the sieves without being subject to cleaning action. To increase the capacity and efficiency of the cleaning mechanism, it is desirable to provide a mechanism for maintaining the threshed grain in contact with the sieves.